Field
Embodiments disclosed herein generally relate to devices and methods for manipulating and recording accommodation in the eye.
Description of the Related Art
Accommodation is the process whereby the young eye changes focus from distance to near. This occurs through a contraction of the ciliary muscle inside the eye. This ciliary muscle contraction causes the lens in the young eye to change shape, which increases the optical power of the eye. The normal accommodative response is rapid in the young eye. The young eye can change focus within about 100-200 milliseconds.
Accommodation is progressively lost with increasing age in the condition called presbyopia. Presbyopia is due to a progressive age-related increase in stiffness of the lens. In humans, accommodation can be produced by having subjects look from a distant target to near-reading text positioned progressively closer to the eyes (known as visual stimulus elicited accommodation). In visual stimulus elicited accommodation, the subject perceives the near object, perceives that the near object (in this case, text) is out of focus and attempts to make the near object clear by accommodating. In presbyopes (persons affected by presbyopia), the subject would perceive the near object is out of focus, but they would not be able to accommodate to change their focus to get the near object in clear focus.
How the eye accommodates, why this physiological function is lost with increasing age and trying to understand if accommodation can be restored in presbyopes is an area of significant basic science, clinical and industry research. Such research is undertaken on human subjects as well as on animal models including non-human primates, especially rhesus monkeys. Rhesus monkeys accommodate in a very similar fashion to the way humans do. Rhesus monkeys also develop presbyopia.
A significant challenge in this area of clinical and laboratory research is how to stimulate accommodation either in human subjects or in animal models. Stimulating accommodation can be challenging for many reasons. For example, in conscious human subjects although presenting near reading text may represent a stimulus to accommodate, the subjects may simply choose not to accommodate or they may not elicit a strong effort to accommodate. Similarly, in animal models, if the animals are anesthetized, it can be challenging to stimulate accommodation.
In both humans and animal models, accommodation can be stimulated by applying drugs, such as pilocarpine, directly to the eye. This produces an accommodative response because the drugs diffuse into the eye and cause the ciliary muscle in the eye to contract. However, drug stimulated accommodation may be very slow relative to the natural accommodative response. In some examples, the drug stimulated accommodation can take 30-45 minutes to achieve a maximum. When compared to the previously described 100-200 milliseconds for natural accommodation to occur, known drug induced accommodation techniques appear inadequate for studying natural accommodation. Further, in current drug stimulation models, the accommodation response can only be elicited a single time in each experimental session.
In animal models where a dynamic accommodative response is desired, complex, lengthy and invasive surgical procedures are required to stimulate dynamic accommodative responses with electrical stimulation. As such, the complexity and expense of the procedure, ethical concerns and danger to the animal all act to limit dynamic accommodation experimentation.
Thus, there is a need for safe and effective exogenous control of accommodation in both humans and animal models.